Download 6.4_EVOLUTION_DIVERSITY OF LIFE NOTES_3_Part 2

Evolution
Diversity of Life
Part 2
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Darwin’s Theory of
Evolution
Organisms Change Over Time
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Common Descent with
Modification



Darwin proposed
that organisms
descended from
common ancestors
Idea that
organisms change
with time,
diverging from a
common form
Caused evolution
of new species copyright cmassengale
3
Natural Selection



Driving force for
evolution
During the struggle for
resources, strongest
survive & reproduce
Idea that at least
some of the
differences between
individuals, which
impact their survival
and fertility, are
inheritable
.
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Origin of Species
Darwin Presents His Case
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Publication of “On The Origin
of Species”


Upon His Return To England, Darwin
Developed His Observations Into
The Theory of Evolution
But He Did Not Publish For 25
Years –
Why?
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Publication of “On The Origin
of Species”
Darwin Knew That His Theory
Would Be Extremely Controversial
And Would Be Attacked
 His Theory Challenged Established
Religious & Scientific Beliefs,
Particularly About The Creation Of
Man

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Publication of “On The Origin
of Species”

He Refused To Publish Until
He Received An Essay From
Alfred Wallace
– Fellow Naturalist
– Independently Developed
The Same Theory
– After 25 Years, Someone
Else Had Come To The
Same Conclusions From
Their Observations Of
Nature
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Wallace’s Contribution
• Alfred Russel Wallace
Independently came to
same Conclusion as
Darwin that species
changed over time
because of their struggle
for existence
• When Darwin read
Wallace’s essay, he knew
he had to publish his
findings
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Publication of “On The Origin
of Species”
Darwin Presented Wallace’s Essay &
Some Of His Work At A Scientific
Conference of the Linnaean Society
in July of 1858
 Then He Started On his book
“Origin of Species”
 It Took Darwin 18 Months To
Complete The Book

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Natural Variation and
Artificial Selection
Abandoned The Idea That Species
Were Perfect & Unchanging
 Observed Significant Variation in
All Species Observed
 Observed Farmers Use Variation To
Improve Crops & Livestock
 Called Selective Breeding

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Natural Variation and
Artificial Selection
 Natural
Variation
– Differences Among Individuals Of
A Species
 Artificial
Selection
– Selective Breeding To Enhance
Desired Traits Among Stock or
Crops
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Natural Variation and
Artificial Selection
Key Concept:
In Artificial Selection, Nature
Provided The Variation Among
Different Organisms, And
Humans Selected Those
Variations That They Found
Useful
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Origin of Species
Concepts and Controversy
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Evolution By Natural Selection
Concepts
The Struggle for Existence
(compete for food, mates, space,
water, etc.)
 Survival of the Fittest (strongest
able to survive and reproduce)
 Descent with Modification (new
species arise from common ancestor
replacing less fit species)

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Survival of the Fittest

Fitness
– Ability of an Individual To
Survive & Reproduce

Adaptation
– Inherited Characteristic That
Increases an Organisms Chance
for Survival
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Survival of the Fittest
 Adaptations
Can Be:
– Physical
»Speed, Camouflage, Claws,
Quills, etc.
– Behavioral
»Solitary, Herds, Packs,
Activity, etc.
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Survival of the Fittest
 Fitness
Is Central To The
Process Of Evolution
 Individuals With Low Fitness
– Die
– Produce Few Offspring
Survival of the Fittest
AKA Natural Selection
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Survival of the Fittest
Key Concept
Over Time, Natural Selection
Results In Changes In The
Inherited Characteristics Of
A Population. These Changes
Increase A Species Fitness In
Its Environment
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Natural Selection
 Cannot
Be Seen Directly
 It Can Only Be Observed As
Changes In A Population Over
Many Successive Generations
– Radiation
– Fossil Record
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Descent With Modification
 Takes
Place Over Long Periods
of Time
 Natural Selection Can Be
Observed As Changes In
– Body Structures
– Ecological Niches
– Habitats
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Descent With Modification
 Species
Today Look Different
From Their Ancestors
 Each Living Species Has
– Descended
– With Changes
– From Other Species
– Over Time
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Descent With Modification
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Descent With Modification
Implies
– All Living Organisms Are Related
– Single Tree of Life
»DNA, Body Structures, Energy
Sources
 Common Descent
– All Species, Living & Extinct,
Were Derived From Common
Ancestors copyright cmassengale
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
Major Problem in Darwin’s
Theory
• No mechanism to explain
natural selection
• How could favorable
variations be transmitted to
later generations?
• With the rediscovery of
Mendel’s work in the first
half of the 20th century,
the missing link in
evolutionary theory was
.
found
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Opposition to Evolution
• The upheaval
surrounding evolution
began with Darwin’s
publication of On the
Origin of Species By
Means of Natural
Selection
• The debate continues
nearly 150 years later
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Theory of Evolution
Today
Supporting Evidence
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Homologous Structures
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Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
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Similarities in DNA Sequence
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Evolution
of
pesticide
resistance
in response
to
selection
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Evidence for Evolution – Evolution Observed
Evolution of drug-resistance in HIV
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Evidence for Evolution – Evolution Observed
Selection against small guppies results in an increase in
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average size
Evolutionary
Time Scales
Macroevolution:
Long time scale
events that
create and
destroy species.
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Evolutionary
Time Scales
Microevolution:
Short time scale
events (generationto-generation) that
change the
genotypes and
phenotypes of
populations
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Evidence of Evolution
Key Concept
Darwin Argued That Living Things
Have Been Evolving On Earth For
Millions of Years. Evidence For This
Process Could Be Found In:
– The Fossil Record
– The Geographical Distribution of
Living Species
– Homologous Structures of Living
Organisms
– Similarities In
Early
Development 37
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Fossil Record
Earth is Billions of Years Old
 Fossils In Different Layers of Rock
(sedimentary Rock Strata) Showed
Evidence Of Gradual Change Over
Time

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Geographic Distribution of
Living Species

Different Animals
On Different
Continents But
Similar Adaptations
To Shared
Environments
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Homologous Body
Structures
 Scientists
Noticed Animals With
Backbones (Vertebrates) Had
Similar Bone Structure
 May Differ In Form or Function
 Limb Bones Develop In Similar
Patterns
»Arms, Wings, Legs, Flippers
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Homologous Body
Structures
Structures That Have Different
Mature Forms But Develop From
The Same Embryonic Tissues
 Strong Evidence That All FourLimbed Animals With Backbones
Descended, With Modification,
From A Common Ancestor
 Help Scientist Group Animals

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Homologous Body
Structures
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Homologous Body
Structures

Not All Serve Important Functions
– Vestigial Organs
» Appendix In Man
» Legs On Skinks
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Similarities In Early
Development
Embryonic Structures Of Different
Species Show Significant
Similarities
 Embryo – early stages of
vertebrate development

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Human Fetus – 5 weeks
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Chicken
Turtle
Rat
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Review
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Darwin's Theory
1.
2.
Individual Organisms In Nature
Differ From One Another. Some
Of This Variation Is Inherited
Organisms In Nature Produce
More Offspring Than Can Survive,
And Many Of These Offspring Do
No Reproduce
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Darwin's Theory
3.
4.
Because More Organisms Are
Produced Than Can Survive,
Members Of Each Species Must
Compete For Limited Resources
Because Each Organism Is Unique,
Each Has Different Advantages &
Disadvantages In The Struggle For
Existence
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Darwin's Theory
5.
6.
Individuals Best Suited To Their
Environment Survive & Reproduce
Successfully – Passing Their Traits To
Their Offspring.
Species Change Over Time. Over Long
Periods, Natural Selection Causes
Changes That May Eventually Lead To
New Species
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Darwin's Theory
7.
8.
Species Alive Today Have
Descended With Modifications
From Species That Lived In The
Past
All Organisms On Earth Are
United Into A Single Tree Of Life
By Common Descent
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